This invention relates to a solder member for printed wiring boards, and more particularly to a solder member having an excellent soldered joint strength to a connection terminal of a conductor pattern in a printed wiring board.
Heretofore, a ball-shaped solder member has mainly been used as a joint member for electrically connecting conductive members of the printed wiring board to each other. And also, the ball-shaped solder member is used for connecting and fixing the printed wiring board to a remote member such as mother board or the like. Such a solder member is a solder ball mainly composed of a solder (Pbxe2x80x94Sn). The solder ball joins to not only the connection terminal of the printed wiring board such as pad, land for through-hole or the like but also the remote member to conduct an electrical connection between the connection terminal and the remote member.
In general, as shown in FIG. 1, the printed wiring board for mounting an electronic part is a substrate 6 to be connected to a mother board 2 through a ball-shaped solder member 4 for external connection. On the substrate 6 are formed connection terminals 8 corresponding to a conductor pattern by etching a copper foil to form a patterned copper layer 9 and then covering a surface of the copper layer 9 with a plated layer 10 formed through an electroless plating process. The plated layer 10 is an electroless Ni/Au plated layer usually formed by electroless Ni plating and electroless Au plating. A ball grid array corresponding to the conductor pattern is formed by disposing a solder member 4 on each of the connection terminals 8.
In the above conventional printed wiring board, however, the joining property between the solder member 4 and the connection terminal 8 is low. Particularly, the joint strength further lowers when the board is held under a high temperature condition over a long time. That is, as shown in FIG. 1, when the solder member 4 is joined to the connection terminal 8 by fusion, tin (Sn) oozes out from the solder onto a surface of the electroless Ni/Au plated layer 10 to thereby form Nixe2x80x94Sn layer 12 between the solder member 4 and the plated layer 10. Phosphorus (P) included in the electroless Ni plated layer elutes out from the plated layer 10 and rapidly permeates and diffuses into the Nixe2x80x94Sn layer 12. As a result, a phosphorus concentration in the Nixe2x80x94Sn layer 12 becomes high and the joint strength between the solder member 4 and the connection terminal 8 lowers to cause the peeling of the solder member from the connection terminal and hence an electrically connection reliability therebetween is degraded. On the other hand, it is considered to remove phosphorus from the electroless Ni plated layer, but in this case, the precipitation of the electroless Ni plated layer becomes ununiform.
In view of the above conventional problems, the invention is to provide a solder member having an excellent soldered joint strength to the connection terminal.
A first aspect of the invention lies in a solder member for external connection joined to a connection terminal formed on a surface of a printed wiring board corresponding to a conductor pattern and having an electroless Ni/Au plated layer, characterized in that the member is comprised of a solder containing finely powdered copper.
In this invention, it is preferable that the solder contains 0.1-20% by weight of copper, and the solder member is a solder ball, and the electroless Ni/Au plated layer contains 3-12% by weight of phosphorus.
A second aspect of the invention lies in a solder member for external connection joined to a connection terminal formed on a surface of a printed wiring board corresponding to a conductor pattern and having an electroless Ni/Au plated layer, characterized in that the member is comprised of a solder containing finely powdered copper and platinum.
In this invention, it is preferable that the solder contains 0.1-20% by weight of copper and 0.01-20% by weight of platinum or further, if necessary, 0.001-5% by weight of gold or 0.01-3% by weight of silicon, and the solder member is a solder ball, and the electroless Ni/Au plated layer contains 3-12% by weight of phosphorus.
A third aspect of the invention lies in a solder member for external connection joined to a connection terminal formed on a surface of a printed wiring board corresponding to a conductor pattern and having an electroless Ni/Au plated layer, characterized in that the member is comprised of a solder containing finely powdered copper and zinc.
In this invention, it is preferable that the solder contains 0.1-20% by weight of copper and 0.01-20% by weight of zinc or further, if necessary, 0.001-3% by weight of iron, and the solder member is a solder ball, and the electroless Ni/Au plated layer contains 3-12% by weight of phosphorus.
A fourth aspect of the invention lies in a solder member for external connection joined to a connection terminal formed on a surface of a printed wiring board corresponding to a conductor pattern and having an electroless Ni/Au plated layer, characterized in that the member is a solder ball consisting of a core made of at least one metal selected from copper, nickel and cobalt and a solder layer covering the metal core.
In this invention, it is preferable that the metal core has a diameter of 100-800 xcexcm, and the electroless Ni/Au plated layer contains 3-12% by weight of phosphorus.
A fifth aspect of the invention lies in a solder member for external connection joined to a connection terminal formed on a surface of a printed wiring board corresponding to a conductor pattern and having an electroless Ni/Au plated layer, characterized in that the member is comprised of a copper ball, a platinum layer covering the copper ball and a solder layer at least partly covering the platinum layer.
In this invention, it is preferable that the copper ball has a diameter of 100-800 xcexcm, and the platinum layer has a thickness of 0.05-10 xcexcm, and the solder layer has a thickness of more than 0 xcexcm but not more than 150 xcexcm, and the electroless Ni/Au plated layer contains 3-12% by weight of phosphorus.
A sixth aspect of the invention lies in a solder member for external connection joined to a connection terminal formed on a surface of a printed wiring board corresponding to a conductor pattern and having an electroless Ni/Au plated layer, characterized in that the member is comprised of a column made of at least one metal selected from copper, nickel, palladium, cobalt and platinum and a solder layer at least partly covering a surface of the metal column.
In this invention, it is preferable that the metal column is a cylindrical form and has a diameter corresponding to 60-97% of a diameter of the solder member, and the solder layer is the same face as at least one of two flat faces or both faces of the column located opposite to each other and parallel thereto, and the flat face of the metal column has a smoothness of 10 xcexcm, and the diameter of the metal column is smaller than a width of the connection terminal, and the electroless Ni/Au plated layer contains 3-12% by weight of phosphorus.